The Path To Underfloor Heating with Compatible Flooring
A lot of planning goes into designing an underfloor heating (UFH) system which will work efficiently and give the householder years of service. Many factors are taken into consideration during the design process including calculating the heat loss from the building, choice of heat source and floor construction. This means that when it comes to installing the UFH system, these issues will have been addressed already.
However, frequently the homeowner does not know how they want the floors finished, until they come to the point of decorating, often a long time after the UFH was installed. Fortunately UFH is compatible with most types of floor finish, although a little care needs to be taken to get maximum benefit from the heating system.
With consumers increasingly concerned about keeping energy costs low and cutting carbon emissions, it is worth bearing in mind that their choice of floor finish and how it is fitted will have an impact. The objective of any heating system, is to achieve as low a flow temperature as possible while still being able to heat the building - not always practical with radiators since these would need to be oversized. UFH works well with modern condensing boilers since the low flow temperature keeps the boiler in condensing mode thereby maximising its efficiency. Similarly, if for example heat pumps are being used as the heat source, then the low flow temperatures demanded by the UFH system increase their efficiency dramatically, with 30% better efficiency than oversized radiators with a ground source heat pump and 20% better efficiency with an air source heat pump.
There are a few basic rules to follow to ensure trouble free flooring.
Contact
All floor finishes should be in good contact with the floor, for example with tiled floors the dot and dab method of fixing tiles should never be used - this is not good practice anyway - and tile adhesive should be used to cover the entire area under the tile. This way there is extremely good contact with the screed below and the surface of the floor which means the UFH system can potentially run as low as 30°C to 35°C, depending on the heating requirement of the room and the pipe spacing.
Flexibility
All buildings flex and move as they warm and cool during a day. The same applies to floor screeds which expand and contract as they warm up and cool. The actual amount of expansion is small but significant enough, and therefore expansion joints should be included in the screed into which the UFH pipework is embedded.
As a rule of thumb these expansion joints should be included every 40m2 or every eight linear metres and at this point the pipe should be sleeved 300mm to each side of the joint. Where tiles or similar floor finishes are being 'fixed' to the floor with adhesives then flexible adhesives suitable for use with UFH should be used. This allows for movement of the floor beneath the tiles since their rate of thermal expansion will be slightly different. The insulation strip around the screed, as well as contributing to the thermal efficiency, also absorbs the screed expansion and contraction.
Moisture
Before the flooring is laid the concrete and screed must be allowed to fully cure and dry. Curing times vary dependent on the type of screed so please check with the contractor/specifier.
After the concrete and screed have cured it will still need to dry out. The accepted figure for natural drying is 1mm per day, however this is dependant on the ambient weather conditions.
Many people use the UFH to speed the drying of the screed. This must be slowly so as not to drive moisture out of the screed too fast and at least 21 days from the screed being laid or seven days for an anhydrite screed. In either case the manufacturer/supplier should be contacted for their advice. The initial starting temperature of the UFH system should not be more than 15°C above the unheated screed temperature. It is also advisable to stabilize this temperature for a few days prior to gradually increasing the flow temperature by 5°C per day, until the desired temperature of the UFH system is reached.
With wooden floors there is always a bit of movement as the moisture content varies within the wood. During the heating season the wood tends to 'dry' as it is warmed and in the summer, when the heating is off, it tends to expand as moisture is absorbed into the floor. However, by following a few simple guidelines wooden floors can be successfully integrated with UFH.
The moisture content of the wood when installed should be around 6% to 9%. If the timber has not been double kiln dried then it can be spread and laid loose on top of the warmed screed to condition it, and the lower moisture levels are achieved.
Ideally the timber should have a thickness to board width ratio of about four so if the board is 20mm thick then the maximum width should be about 80mm.
Always liaise with your flooring supplier since virtually all suppliers have ranges of products suitable to use in conjunction with UFH.
To conclude, UFH is compatible with most flooring types but if you have any queries then Continental Underfloor Heating has an expert technical team on hand to answer any questions. For more information log onto www.continental-ufh.com or call 0845 108 7001.
